How is processing a thousand images different in kind from processing one? As long as you want to perform the same operation on every frame, it's a trivially parallelizable task. The gimp is happy to run headless with a script, and IIRC After Effects has built-in support for running a render farm. Building a little DIY cluster isn't building camera equipment out of legos, but if you're trying to make a living off YouTube videos it's not out of reach either.
Because the tuning and tweaks for one image aren't necessarily the tuning and tweaks for all images. Yes - you can say "do this to all of these" but if you have a series of still images, "do this to all of these" will get you close, not perfect. You're effectively arguing that the log average is good enough, and it's not.